When I worked at Activision, one of the vice presidents told me that when he suggested a new feature to a game designer, there was a three-state process:

1. "It's impossible!"
2. "It's too hard."
3. "It's on your desk."

Note that the process doesn't have anything to do with getting a commitment out of the game designer. Just plant the seed and occasionally ask if he's figured out how to do it yet. If the idea is a good one, it will gnaw at the designer, and eventually a solution will appear as if by magic.

That was great management. The designer's own desire that his product be cool was the only tool required.